1. Field Of The Invention
This invention relates generally to compositions from which writing instruments such as crayons are fabricated and, in particular, to solid marking compositions which incorporate polyethylene resins. The invention further relates to marking instruments, such as crayons, fabricated from such compositions.
2. Brief Description Of The Prior Art
It is well known that crayons can be produced from mixtures of waxes, fatty acids, colorants and extenders. When properly formulated, crayons can be used to draw, write or color. They do, however, suffer from poor eraseability, low breaking strength, low softening point, and rapid wear rate.
Some level of improvement has been reported by the incorporation of various additives. For example, U.S. Pat. No. 2,882,246 teaches that the addition of 0.1 to 10% polyethylene increases the melting point. U.S. Pat. No. 3,933,708 teaches that addition of 0.1 to 10% of a high molecular weight polyethylene allows the use of lower melting point paraffin waxes. U.S. Pat. No. 4,212,676 teaches that one may obtain eraseability by combining "emulsifiable" polyethylenes with a mixture of liquid hydrocarbons, while Japan 1983-4751 teaches that it may be obtained by the use of polyacrylates. Offenlegungsschrift 26 13 933 teaches that one must use a mixture of high density polyethylene or polypropylene and low molecular weight (m.w.&lt;10,000) polyethylene, in combination with wax and pigment, in order to provide acceptable properties in a colored pencil.
Although these prior teachings indicate that one may produce generally suitable writing instruments from mixtures of wax and blending agents, none teaches how to provide good eraseability coupled with attractive application characteristics, while still preventing bloom. Bloom is the migration of one or more components to the surface of the crayon which results in the formation of a white-gray surface deposit which obscures the true color of the crayon. It is a serious defect in a crayon, since it not only renders the crayon not aesthetically pleasing, but also makes it more difficult for one to select a crayon of a desired color from among several others. In some cases, bloom can develop on the surface of the layer of the crayon composition which has been applied to the paper or other coloring surface.
None of the prior teachings addresses the problem of how to achieve a proper balance of all properties; namely, eraseability, breaking strength, ease of application, and absence of bloom.
In accordance with the foregoing, it is a general object of the present invention to obtain an improved plastic crayon composition.
A related object is to produce a solid marking composition in which all the desirable properties may be optimized.
A more particular object is to obtain a plastic crayon composition having improved eraseability, ease of application, and strength, while bloom is eliminated.
Another object is to produce a solid marking composition having improved eraseability, ease of application, and strength, and essentially no bloom, without the necessity for including additives for that purpose.
Other objects and advantages of the composition of the present invention will be apparent to those skilled in this art from the following description and the appended claims.